1. Field of the Invention
The present invention relates to a method for measuring a minute current flowing through an electrical element, an inspection method of a semiconductor device employing the current measurement method, a semiconductor device employing the current measurement method, a semiconductor device employing the inspection method, a test element group, and the like. Here, a semiconductor device may be any device which works by utilizing semiconductor characteristics. Examples of semiconductor devices include, in a broad sense, semiconductor elements (including so-called power devices) such as transistors, diodes, and thyristors; integrated circuits such as image sensors, memories, and converters; integrated circuits including any of these semiconductor elements and integrated circuits; and display devices typified by liquid crystal display devices.
2. Description of the Related Art
In recent years, research on thin film transistors using In—Ga—Zn based metal oxide has been brisk (see Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2, for example). The research is proceeding with a view mainly to replacing silicon based thin film transistors used in display devices with thin film transistors using In—Ga—Zn based metal oxide.
By the way, in the case of fabricating semiconductor devices that need charge retention, such as liquid crystal display devices, it is extremely important to know the characteristics of thin film transistors in the off state, e.g., the value of a current flowing between the source and the drain of a transistor in the off state (hereinafter referred to as off-state current), and the like. This is because the parameters of a thin film transistor such as channel length and channel width are determined in accordance with the characteristics of the thin film transistor in the off state.
For now, it has been reported that the off-state current of a transistor using amorphous In—Ga—Zn based metal oxide is less than 10−14 A (see Non-Patent Document 3, for example).